The invention relates to a torque transmission unit having at least one component for transmitting torques via each of two functional areas formed onto the component and causing the torque flow by a formfitting engagement with other elements, at least one of the two functional areas being constructed as a profile, such as longitudinal teeth.
Torque transmission units of this type are disclosed, for example, in U.S. Pat. No. 6,872,143 (=DE 102 20 715) in connection with side shafts and in US 2006/0014587 (=DE 102 37 172) in connection with longitudinal shafts.
In U.S. Pat. No. 6,872,143, two such components are provided for each of the fixed, constant velocity ball joints provided on both ends of the side shaft, on each of which different functional areas formed onto the particular component are provided, which cause the torque flow by formfitting engagement and one of which is constructed as longitudinal teeth.
One component is the joint external part, whose one functional area causing the torque flow by formfitting engagement is a connection pin having formed-on longitudinal teeth, which is provided on the joint external part, and whose other functional area transmitting the torque are the raceways in the joint external part for the balls of the joint.
The second component also having two functional areas for transmitting torque is the joint internal part having formed-on longitudinal teeth in the central internal area as one functional area and having formed-on ball raceways of the joint internal part as the other functional area.
In the torque transmission unit according to US 2006/0014587, a component having two functional areas for transmitting torque is also provided for each of the three joints contained therein, namely a joint internal part having formed-on longitudinal or spline teeth as one functional area and formed-on ball raceways as the other functional area in each case.
In components of this type, i.e., joint parts, for example, the internal teeth are typically broached and the external teeth are typically produced by pounding, milling, or rolling, and the ball raceways are produced by machining or by a non-chip-forming or chipless technique.
To be able to transmit sufficient torque, at least the ball raceways are hardened. These raceways may be inductively hardened and the remaining area, i.e., also the longitudinal teeth, may be left at the basic hardness. This is advantageous for producing longitudinal teeth, but does not permit the high torque values to be transmitted and the desired service life to be achieved, which are required in many cases.
The inductively hardened ball raceways, for example, must be machined hard because of the distortion occurring upon partial hardening after the hardening to achieve the acquired precision, i.e., hard milling or grinding must be performed.
Another known possibility is to first manufacture the teeth in the soft state, to case-harden the entire part, i.e., having formed-on longitudinal teeth, which results in hardening distortion of both the teeth and also the spline teeth, however, which may only be remedied in the longitudinal teeth with additional great effort, namely by hard broaching in the hard layer using corresponding suitable, but costly special machines and tools, for example.